Stepping motor drive circuit

ABSTRACT

A circuit for moving the rotor of a stepping motor from one position to another without vibration or oscillation including means for energizing the magnets of the stepping motor that would normally be energized to move the rotor of the motor from a first position to a second position for a first predetermined period of time, means for energizing the magnets that would normally be energized to return the rotor from the second position to the first position for a second predetermined period of time and means for re-energizing the magnets would normally be energized to move the rotor from the first position to the second position.

ited States Patent 1 Cook et al. 51 May 29, 1973 [54] STEPPING MOTORDRIVE CIRCUIT [75] Inventors: Harold D. Cook, Wheaton; Owen F. PrimarySlmmons,

Davis Des Plaines, both of Att0rney-J. Landes and R, Miller [73]Assignee: Teletype Corporation, Skokie, Ill. 57 ABSTRACT Filedi 3,1966 Acircuit for moving the rotor of a stepping motor [2]] Appl NOJ 570,077from one position to another without vibration or oscillation includingmeans for energizing the magnets of the stepping motor that wouldnormally be ener- U-S. gized to move the rotor of the motor from a firstposi- [51] lnt.Cl ..H02k 37/00 do to a second position for a firstpredetermined [58] Field of Search ..3l8/254, 138, 696, period f time,means for energizing the magnets that 318/685 would normally beenergized to return the rotor from the second position to the firstposition for a second [56] References C'ted predetermined period of timeand means for re-ener- UNITED STATES PATENTS gizing the magnetswouldpormallv be energized to move the rotor from the first position tothe second 3,328,658 7/1964 Thompson ..3l8/138 position 3,345,54710/1967 Dunne ...3l8/l38 3,386,018 5/1968 Smith-Vaniz ..3l8/l38 3Claims, 1 Drawing Figure 34 a! 52 E INPCUT DELAY DELAY j? CIRCUITCIRCUIT s 33 OR w. 26

PIA IB OB Pos o 1 l 42 2o POA KB 05 PIB POB l- I PIA IA 0A 23 PatentedMa 29, 1973 INPUT E DELAY 36 O cmcurr s 33 OR w. 26

ATT Y 1 STEPPING MOTOR DRIVE CIRCUIT This invention relates to steppingmotor drive circuits and more particularly to circuits for operatingstepping motors at high rates of speed.

In recording devices stepping motors are often em ployed to move therecording medium because the inherent incremental movement of steppingmotors affords precise control over the positioning of the recordingmedium and therefore allows a maximum amount of recording per unitlength of recording medium. As recording speeds have increased it hasbecome necessary to operate the stepping motors used in recordingdevices at increasingly higher rates of speed. This has caused problemssince, stepping motors which are operated at high rates of speed tend tovibrate or oscillate excessively upon reaching a position to which theyare stepped.

Accordingly, an object of this invention is to provide a circuit foroperating stepping motors at high rates of speed.

Another object of this invention is to provide a cir' cuit for causing astepping motor to step from one position to another position at highspeed with a minimum of vibration.

In a preferred embodiment of the invention these and other objects areachieved by applying a pulse to a stepping motor which causes thestepping motor to step in a first direction. After this pulse is appliedfor a predetermined period of time, a reverse pulse which normally wouldcause the stepping motor to step in the opposite direction is applied.After the reverse pulse has been applied for a second predeterminedperiod of time the original pulse is reapplied. This causes the steppingmotor to move from a first position to a second position rapidly withoutvibration since any tendency of the motor to vibrate upon reaching itsnew position is damped by the reverse pulse.

A more complete understanding of the invention may be had by referringto the following detailed description when taken in conjunction with thedrawing wherein there is schematrically illustrated a stepping motordrive circuit employing the present invention.

In the ensuing description of the operation of the circuit shown in thedrawing the terms positive" and negative potentials are used to identifythe relative voltages being employed. It should be understood that inactual practice such potentials need not be positive or negative but, byway of example, could be volts and 6 volts or +6 volts and 0 volts,respectively, etc. depending on the particular circuit componentsutilized. It is believed, however, that the use of the terms positive"and negative will serve to differentiate the relative potentials usedand will facilitate an understanding of the operation of the circuit.

In the drawing there is schematically illustrated a stepping motor 10which is of the fully reversible type. Preferably the stepping motor 10is of the type having a plurality of stator electromagnets arranged in acircular array around a rotatably mounted rotor. The rotor is magnetizedso that various points on the rotor are of north or south magneticpolarity. The stator magnets are wound in a bifilar manner so that theymay be polarized either identically with or oppositely to the polarityof any given portion of the rotor at any given time.

When the rotor of the stepping motor 10 is held in any given positionthe stator magnet directly in line with a particular portion of therotor is magnetized to the opposite polarity of that portion of therotor whereas other stator magnets are magnetized to the same polarityas that particular portion of the rotor. When it is desired to move therotor in a given direction this other stator magnet is magnetized to anopposite polarity from the polarity of the particular section of therotor and the magnet which has been aligned with the particular sectionof the rotor is magnetized to the same polarity as the polarity of thatparticular section of the rotor. This causes the particular section ofthe rotor to be repelled away from the magnet with which it had beenaligned and to be attracted toward the other stator magnet in adirection of desired rotation of the rotor. Therefore, the particularsection of the rotor is quickly and positively driven by magnetic actionthrough an incremental step of rotation and into alignment with a statormagnet one incremental step away from the one with which it had beenaligned. This action is repeated around the periphery of the rotor atvarious points so that more than one magnet serves to move the rotorthrough each incremental step.

Although any suitable stepping motor of the type described may beemployed in conjunction with the present invention, a suitable steppingmotor for use with the invention is the motor sold by the SuperiorElectric Company of Bristol, Connecticut under the trademark SLO-SYN andidentified by that company as Type 8825-1002.

Also shown in the drawing are two boxes 11 and 12 which are labeled FF.These boxes represent flip-flop circuits of the type disclosed in FIG. 2of a copending application, Ser. No. 469,522, filed in the name of H. D.Cook on July 6, 1965. The particular internal circuitry of theseflip-flops forms no part of this invention and reference may be had toapplication Ser. No. 469,522 for the details of their operation. Itshould be noted, however, that these flip-flops are of the type in whicha positive trigger input must be gated with a positive direct currentpriming potential before the trigger input has any affect on theoperation of the flip-flop. For convenience the two states or levels ofthe flip-flop are designated as 0 and 1. The priming inputs for a levelof the flip-flop are designated by the letter P. The priming input whichis gated with a particular trigger input is designed in the drawing bythe same letter A or B at both the trigger and the priming inputs of theflip-flop. For example, a trigger input used to set a flipflop to its 0"level is designated on the drawing as 08 or 0A and this trigger input isgated with a priming input POB or POA, respectively. The outputs of theflipflops are labeled merely 0 or 1 with a positive output potentialbeing obtained from the output to which the flip-flop is set and anegative potential being obtained from the other output at the sametime.

The outputs of the flip-flops 11 and 12 are used to control theoperation of the stepping motor 10 through a plurality of leads 13, 14,15 and 16 which extend to the magnets in the stepping motor 10 and whichare used to pass current at the output potentials of the flipflops l1and 12 through the magnets of the stepping motor 10 to a source ofground potential connected to a common lead 17 of the stepping motor 10.For convenience and simplicity of description of the operation of theflip-flops 11 and 12 in controlling the magnets of the stepping motor 10will first be described in the manner employed in the prior art, afterwhich the changes in the operation of the flip-flops which are made inthe practice of the present invention will be explained.

Assume first that both the flip-flops 11 and 12 are in their levels orstates. At this time an output lead 20 connected to the 0 output of theflip-flop 1 1 and also connected to the priming inputs FDA and P18 ofthe flip-flop 12 is at positive potential whereas an output lead 21connected to the l output of the flip-flop 11 and also connected to thepriming inputs P08 and P1A of the flip-flop 12 is at negative potential.Thus, the triggering inputs 0A and 1B of the flip-flop 12 are primed bythe output of the flip-flop 11 whereas the trigger inputs 0B and 1A ofthe flip-flop 12 are not primed since the l output of the flip-flop 11is negative.

Since the flip-flop 12 is also in 0 state a positive potential isapplied to a lead 22 connected to its 0 output. The lead 22 is alsoconnected to the priming inputs P 1A and POB of the flip-flop 11 andaccordingly the triggering inputs 1A and 0B of the flip-flop 11 areprimed. A lead 23 connected to the 1 output of the flip-flop 12 and alsoconnected to the priming inputs P18 and POA of a flip-flop 11 is, ofcourse, maintained at negative potential when the flip-flop 12 is in its0 state and, accordingly, the triggering inputs 1B and 0A of theflip-flop 11 are not primed.

Assume that it is desired to advance the stepping motor in a directionarbitrarily selected as forward. A positive pulse is applied to aforward lead 25 which is connected to both the 1A and 0A triggeringinputs of both of the flip-flops 11 and 12. The flip-flop 12 is primedto its 0 level by the output of the flip-flop 11 but is not primed toits l level since the potential on the lead 21 is negative. Accordingly,when the positive pulse appears on the lead 25 the flip-flop 12 would beset to its 0 state except that it already is in its 0 state. Therefore,the positive potential appearing on the lead 25 has no effect whatsoeveron the flip-flop 12.

On the other hand, the flip-flop 11 is primed to its 1 state by thepositive potential of the 0 output of the flip-flop 12 which is appliedthrough the lead 22 to the PlA priming input of a flip-flop 11. Thus,when the positive potential is applied through the lead 25 to the 1Atriggering input of the flip-flop 11, the flip-flop 11 is driven to its1 state. Therefore, as a result of a positive potential being applied tothe forward lead 25, the flip-flops 11 and 12 change from a 0,0condition to a 1,0 condition (the flip-flops being referred to innumerical order).

As a result of the change of state of the flip-flops 11 and 12, positivepotential is no longer applied to the leads 14 and 16 extending to thestepping motor but is instead applied to the leads l3 and 16 which areconnected to the l output of the flip-flop 11 and the 0" output of theflip-flop 12, respectively. Conversely, the leads 14 and 15, which areconnected to the 0" output of the flip-flop 11 and the 1" output of theflip-flop 12, are driven to negative potential. This change in thepotentials applied to the input leads 13 through 16 of the steppingmotor 10 is the precise change required to cause the rotor of thestepping motor 10 to rotate from the position with which it had beenassociated to the magnets next adjacent that position in the directionarbitrarily designated forward.

When it is desired to rotate the rotor of the stepping motor 10 anotherstep in the forward direction, a secand positive pulse is applied to theforward lead 25. Since the flip-flops 11 and 12 are in a 1 and a 0state, respectively, the l output of the flip-flop 11 is at a positivepotential and thus primes the priming inputs P03 and PIA of theflip-flop 12 through the lead 21. The flip-flop 12, however, primes thepriming inputs P1A and FOR of the flip-flop 11 through the lead 22connected to its 0 output. Thus, when the positive potential is appliedto the lead 25 the flip-flop 11 does not change state since it isalready in the 1 state to which it is primed. The flip-flop 12, however,does change state since it is primed to its 1 state by the 1 output ofthe flip-flop 11 and since it is in its 0 state. Accordingly, upon theapplication of a second positive potential to the forward lead 25 theflip-flops 11 and 12 change from a 1,0 condition to a 1,1 condition.This change changes the positive and negative potentials applied to theleads 15 and 16 of the stepping motor 10 and accordingly, the steppingmotor is advanced one step in the forward direction.

When the flip-flops 11 and 12 are both in the l" state, positivepotentials are applied to the leads 21 and 23 from the 1 outputs of theflip-flops 11 and 12, respectively. Since the leads 21 and 23 areconnected to the POA and PlA priming inputs of the flip-flops 11 and 12,respectively, a third positive pulse on the forward lead 25 changes thestate of the flip-flop 11 from its l state to its 0 state but has noeffect whatsoever on the flip-flop 12 since that flip-flop is already inthe 1 state to which it is primed. Accordingly, when a third positivepotential is applied to the forward lead 25 the flip-flops 11 and 12change from a 1,1 condition to a 0,1 condition, which results in achange of the potentials applied to the leads 13 and 14 and therebycauses the stepping motor 10 to advance one step in the forwarddirection.

When the flip-flops 11 and 12 are in their 0 and l states, respectively,the flip-flop 11 is primed to the 0 state by the 1 output of theflip-flop 12 and the flip-flop 12 is primed to the 0 state by the 0output of the flip-flop 11. Accordingly, a fourth positive potentialapplied to the forward lead 25 has no effect on the fiip-flop 11 whichis already in the 0 state but instead causes the flip-flop 12 to changefrom its 1 state to its 0 state. This return the flip-flops 11 and 12 totheir initial condition (0,0) and also returns the potentials applied tothe leads 13 through 16 to their initial conditions. Thus, the inputpotentials applied to the magnets of the stepping motor 10 are returnedto their original state.

From the foregoing description it will be evident that as positivepotentials are applied to the lead 25 the condition of the flip-flopschange in a regular pattern. This pattern is shown in the followingtable wherein a positive potential applied to the forward lead 25 alwayscauses the flip-flops to change to the next lower state on the table:

If it is desired to have the rotor'of the stepping motor 10 rotate in adirection opposite to the forward direction, that is, in a reversedirection, it is necessary to have the flip-flops 1 1 and 12 change tothe state which is next above any given state on the foregoing chart.This is accomplished by applying a positive potential to the reverselead 26.

Assume that the flip-flops 11 and 12 are both in the 0 state. The PlBtriggering input of the flip-flop 12 is primed through the lead 20 bythe 0 output of the flip-flop 11, whereas the POB triggering input ofthe flip-flop 11 is primed through the lead 11 by the 0 output of theflip-flop 12. Thus, a positive pulse on the reverse lead 26 which isconnected to the triggering inputs 1B and 0B of both of the flip-flopsl1 and 12 causes the flip-flop 12 to change to its l state but has noeffect whatsoever on the flip-flop 11. Therefore, the flip-flops changefrom the 0,0 state to the 0,1 state, that is, they proceed to the nexthigher level in the foregoing chart. From this and from the foregoingdescription of the operation of the flip-flops l1 and 12 in response topositive inputs on the forward lead 25, it should be evident that asuccession of positive inputs on the reverse lead 26 will cause thestate of the flipflops to proceed in an upwardly direction on theforegoing chart.

In conventional operation of the stepping motor 10, a positive potentialis merely applied to the lead 25 whenever the rotation of the rotor isin the forward direction is desired whereas a positive potential ismerely applied to the lead 26 whenever rotation of the rotor in thereverse direction is desired. It has been found, however, that operatingthe stepping motor 10 in this manner is not wholly satisfactory whenvery rapid steps of the rotor of the stepping motor are desired. Themajor difficulty experienced in conventional operation of the steppingmotor 10 is a severe vibration of the rotor of the stepping motor uponreaching a new position. Thus, instead of rapidly and positivelyadvancing from the first position to a second position and thenremaining in a second position, the rotor moves from the first positionto the second position and then vibrates or oscillates about the secondposition for a relatively long period of time. Such vibration oroscillation about a new position is very undesirable when the steppingmotor 10 is used in conjunction with a recording device to move arecording medium through the device. This is because recording on therecording medium cannot take place until the recording medium isstationary, and thus recording on the recording medium must be delayeduntil the rotor of the stepping motor 10 stops vibrating or oscillatingabout a new position.

It has been found that the above described difficulty in theconventional operation of the stepping motor 10 can be almost completelyeliminated if the circuit 30 which is attached to the leads 25 and 26through a reversing switch 31 is used to operate the flip-flops 11 and12. The circuit 30 includes a pair of delay circuits 32 and 33 of a typewhich emit a positive output pulse a predetermined time after theapplication of a positive input pulse. Thus, assuming that the reversingswitch 31 connects a lead 34 which is attached to the output of thedelay circuit 32 directly to the reverse lead 26 and connects a lead 35attached to the output of an OR-gate 36 directly to the forward lead 25,a positive input pulse appearing on the input of the circuit 30 isapplied to the forward lead 25 through the OR-gate 36 and thus causesthe states of the flip-flops 11 and 12 to move one step downwardly onthe foregoing chart. The potentials applied to the leads 13 through 16are thereupon changed in the manner which causes the rotor of thestepping motor to advance toward the next position in the forwarddirection.

The positive pulse on the input of the circuit 30 also triggers thedelay circuit 32 and accordingly, after a predetermined period of timedetermined by the internal characteristics of the circuit 32, the delaycircuit 32 produces a positive output pulse. This pulse is appliedthrough the lead 34 and the reversing switch 31 to the reverse lead 26and accordingly causes the states of the flip-flops l1 and 12 to moveupwardly one step on the foregoing chart, that is, back to the statethey were in before the input pulse was applied to the input of thecircuit 30.

The change of the state of the flip-flops l1 and 12 causes thepotentials applied to the leads 13 through 16 to be returned to theirinitial condition. Thus, the mag nets of the stepping motor 10 no longerurge the rotor to move from the first position to the second position inthe forward direction but instead urge the rotor to move back from thesecond position to the first position. This produces a retarding effecton the motion of the rotor of the stepping motor 10 and thus serves todamp that motor and to slow the rotor of the stepping motion as itapproaches the second position.

The output of the delay circuit 32 in the circuit 30 also is applied toa delay circuit 33 which, after a predetermined time determined by theinternal characteristics of the delay circuit 33 applies a positivepulse through the OR-gate 36 to the forward lead 25. This causes theflip-flops 11 and 12 to change to a state which is one step downwardlyon the foregoing chart from the state at which they were after the delaycircuit 32 applied its output pulse through the lead 34 to the reverselead 26. That is, the output of the delay circuit 33 causes theflip-flops 11 and 12 to return to the state to which they were drivenwhen the input signal was applied through the OR-gate 36 and the lead 35to the forward lead 25. The effect of the return of the flipflops 11 and12 to the condition in which they cause the rotor of the stepping motor10 to move from the first position to the second position is to causethe rotor of the stepping motor 10 to continue in its movement to thesecond position and to settle in the second position with a minimum ofvibration and oscillation.

The time periods of the initial pulse and the reversing pulse asdetermined by the delay circuits 32 and 33 consume practically theentire time period that it takes for the rotor of the stepping motor 10to move from a firstposition to a second position. For example, it hasbeen found that when the circuit 30 is employed in conjunction with thestepping motor identified above, the reverse pulse which is applied bythe delay circuit 32 should occur approximately 1 millisecond after theinitial input pulse. The final forward pulse which is applied to theforward lead 25 by the delay circuit 33 should also occur approximately1 millisecond after the reverse pulse, at which time the rotor isactually in its new position. The next input signal can then follow thefinal forward pulse by approximately 1 millisecond so that the totaltime period used to complete a movement of the rotor of the steppingmotor 10 from a first position to a second position is approximately 3millisecends.

The function of the reversing switch 31 is to apply the output of theOR-gate 36 to the reverse lead 26 and to apply the output of the delaycircuit 32 to the forward lead 25 whenever it is desired to cause therotor of the stepping motor 10 to move in the reverse direction. Thus,instead of the pulse sequence forward-reverseforward which is applied bythe circuit 30 to cause the rotor of the stepping motor 10 to advancefrom a first position to a second position in the forward directionquickly without vibration or oscillation, a pulse sequencereverse-forward-reverse is applied whenever the reversing switch 31 isoperated thereby causing the rotor to travel quickly from a firstposition to the second position in a reverse direction without vibrationor oscillation.

Although a particular embodiment of the invention is shown in thedrawings and described in the foregoing specification it will beunderstood that the invention is not limited to that specificembodiment, but is capable of modification and rearrangement, andsubstitution of parts and elements without departing from the scope ofthe invention.

What is claimed is:

1. In a stepping motor operating circuit of the type including a pair offlip-flops each having inputs and having outputs connected to the inputsof a stepping motor, a pair of input leads and circuitry interconnectingthe input leads, the outputs of the flip-flops, and the inputs of theflip-flops so that successive pulses on one of the input leads cause theflip-flops to produce output pulses that rotate the stepping motor inone direction and so that successive pulses on the other input leadcause the flip-flops to produce output pulses that rotate the steppingmotor in the other direction, the combination with the input leads of adrive circuit including a pulsing lead, a pair of delay circuits eachhaving an input and an output and means for connecting the pulsing leadto one of the input leads and to the input of one of the delay circuits,for connecting the output of said one of the delay circuits to the otherof the input leads and to the input of the other of the delay circuitsand for connecting the output of said other of the delay circuits tosaid one of the input leads so that a single pulse on the pulsing leadchanges the flip-flops from a first condition to a second conditionthereby energizing the stepping motor to move its rotor from a firstposition to a second position then changes the flip-flops from thesecond condition to the first condition thereby energizing the steppingmotor to move its rotor from the second position to the first positionthen changes the flip-flops from the first condition to the secondcondition thereby energizing the stepping motor to move its rotor fromthe first position to the second position.

2. The combination according to claim 1 further including a reversingswitch connected between the pulsing circuit and the input leads andadapted to cause the pulsing circuit to operate upon the input leads sothat the flip-flops energize the stepping motor in a reverse direction.

3. The combination according to claim 1 wherein said one of the delaycircuits changes the flip-flops from the second condition to the firstcondition after a predetermined period of time and wherein said otherdelay circuit returns the flip-flops to the first condition afterapproximately the same period of time.

1. In a stepping motor operating circuit of the type including a pair offlip-flops each having inputs and having outputs connected to the inputsof a stepping motor, a pair of input leads and circuitry interconnectingthe input leads, the outputs of the flip-flops, and the inputs of theflip-flops so that successive pulses on one of the input leads cause theflip-flops to produce output pulses that rotate the stepping motor inone direction and so that successive pulses on the other input leadcause the flip-flops to produce output pulses that rotate the steppingmotor in the other direction, the combination with the input leads of adrive circuit including a pulsing lead, a pair of delay circuits eachhaving an input and an output and means for connecting the pulsing leadto one of the input leads and to the input of one of the delay circuits,for connecting the output of said one of the delay circuits to the otherof the input leads and to the input of the other of the delay circuitsand for connecting the output of said other of the delay circuits tosaid one of the input leads so that a single pulse on the pulsing leadchanges the flip-flops from a first condition to a second conditionthereby energizing the stepping motor to move its rotor from a firstposition to a second position then changes the flipflops from the secondcondition to the first condition thereby energizing the stepping motorto move its rotor from the second position to the first position thenchanges the flip-flops from the first condition to the second conditionthereby energizing the stepping motor to move its rotor from the firstposition to the second position.
 2. The combination according to claim 1further including a reversing switch connected between the pulsingcircuit and the input leads and adapted to cause the pulsing circuit tooperate upon the input leads so that the flip-flops energize thestepping motor in a reverse direction.
 3. The combination according toclaim 1 wherein said one of the delay circuits changes the flip-flopsfrom the second condition to the first condition after a predeterminedperiod of time and wherein said other delay circuit returns theflip-flops to the first condition after approximately the same period oftime.